This invention relates generally to a Segmented Electrode Development (SED) unit of a printing system and more particularly concerns a compact design for the electrical connection of a SED roll of a SED unit.
In general, the process of electrophotographic printing includes charging a photoreceptor to a substantially uniform potential so as to sensitize its photoconductive surface. Referring to FIG. 1, there is shown a prior art photoreceptor 10. Usually, a scanning light beam 12 scans a scan line 14 on a photoreceptor 10. The photoreceptor 10 rotates and as a result, the scanning light beam scans consecutive scan lines 14 to discharge the photoreceptor 10 and transfer an image onto the photoreceptor. The image on the photoreceptor 10, which is an electrostatic image, is called a latent image. Once a latent image is created on each scan line, toner has to be placed on each individual scan line 14 to be transferred onto a sheet of paper and then heated to permanently fuse to the sheet of papaer.
One method used for transferring the toner onto the latent image, known as Segmented Electrode Development (SED), uses a SED roll 16. Referring to FIG. 2, there is shown a magnified view of the SED roll 16 of FIG. 1. Referring to both FIGS. 1 and 2, SED roll 16 is a cylindrical member which is placed along the photoreceptor 10 and has a plurality of electrodes 18 that are closely spaced along the SED roll 10.
As the photoreceptor 10 and the SED roll 16 rotate, at any given time, one or multiple electrodes 18 which have the closest distance to the photoreceptor 10 will be activated. The activated electrodes 18 generate a toner cloud 19 along their length in a development region near the photoreceptor. The latent image on each scan line 14 has opposite charge to the charge of the toner in the toner cloud 19. Electrostatic fields generated by the latent image attract toner from the toner cloud 19 to develop the latent image.
In order to activate a selected number of the electrode 18, a carbon electrical brush 20 is used. Electrical brush 20 contacts a portion of the SED roll 16. As the SED roll 16 rotates, different electrodes 18 come in contact with the electrical brush 20.
Electrical brush 20 is not a reliable contact to the electrodes 18. When the electrical brush 20, which has a high voltage of about 1000 volts, connects to each electrode 18 or disconnects from each electrode 18 a phenomenon called "arcing" happens. The connection and disconnection of a 1000 volts to and from an electrode cause large sparks. Since there are plurality of electrodes 18, for example 312 electrodes, on a SED roll 16 and the SED roll 16 rotates at a speed in the range of 400 to 600 rpm, the electrical brush 20 withstands an enormous number of sparks,but gradually, the sparks cause the electrical brush 20 and electrodes 18 to wear off. As a result, the electrical brush 20 has a short life span.
The object of this invention is to provide a reliable solution for the electrical connection to a SED roll.